Picornaviruses form all their proteins by proteolytic cleavages. Many other animal viruses, including RNA tumor viruses, togaviruses; myxoviruses, adenovirus and herpes simplex virus, form some of their proteins by cleavage reactions. Thus, understanding the cleavage processes is an integral part of understanding the synthesis of viral proteins and the maturation of virion particles. The translation products from encephalomyocarditis virus (EMC) RNA synthesized in rabbit reticulocyte lysates contain a protease that can cause almost complete cleavage of EMC capsid precursors into capside proteins. We propose to study the detailed function and the characteristics of this viral enzyme. Also, we want to study the properties of the corresponding poliovirus protease and to find a convenient method for in vitro synthesis of poliovirus capsid precursor proteins, the substrate of the viral protease. Another objective of this proposal is to study the involvement of tRNA on the expression of the EMC protease gene. The methods which will be used include protein synthesis in reticulocyte lysates, column chromatography, and SDS-polyacrylamide gel electrophoresis.